Former Siberian policeman Mikhail Popkov, who is already serving a life sentence for the murders of 22 women, has confessed to killing 59 more, police told the Siberian Times.

Nicknamed the “werewolf” of Siberia for the brutality of his methods — he raped women and then killed them with axes, knives or screwdrivers — Mikhail Popkov carried out his bloody rampage between 1992 and 2010 in the Angarsk and Irkutsk regions of Siberia, the paper reported. According to the state news agency Tass, he resigned as a police officer in 1998.

When he was first detained in 2012, the Siberian Times said, he told police his goal was to “cleanse” the streets of prostitutes.

According to Tass, the investigation began when women kept disappearing from public places in Angarsk in the mid-1990s, at the time Popkov was a police officer. Later, authorities started finding mutilated bodies of the women around Irkutsk.

They also found tire tracks from a Niva cross-country vehicle at some of the crime scenes, which ultimately led them to Popkov.

At first he confessed to three murders.

But as police investigated, and as he began talking, the number rose to the 22 for which he was convicted and sentenced in January 2015.

Irkutsk police spokeswoman Karina Golovacheva has told the Siberian Times that Popkov has now confessed to 59 new slayings. “That means, if we add them to the earlier 22, it will be 81 murders in total.” Of the 59 cases, 47 have produced charges. “We are quite sure about the 12 other cases,” Golovacheva told the paper, and “in the nearest future we can bring charges” in the twelve others.

The victims have ranged in age from 17 to 38.

Popkov, according to earlier reports of the case, started his spree when he was a policeman, offering women rides in his police car and then taking them to remote locations and raping and killing them.

After laborious probes, police have found body after body in the places where Popkov told them they were hidden.

The Siberian Times speculated that he was confessing gradually to the killings rather than all at once in hopes of delaying his transfer from a detention prison to a penal colony.

If authorities ultimately confirm 81 as the number of Popkov’s victims, that would make him one of the most prolific serial killers of all time, behind Colombia’s Luis Garavito, a child-killer nicknamed “The Beast” who claimed at least 138 lives in the 1990s, and Pedro López (“The Monster of the Andes”) with 110 proven victims in Colombia, Ecuador and Peru between 1969 and 1980.